1. Field of the Invention
The present invention relates to the field of semiconductor devices and more specifically to patterning of an interlayer dielectric layer.
2. Discussion of Related Art
The fabrication of semiconductor devices with smaller dimensions and the increasing switching speeds of transistors necessitate the use of copper lines and low-k interlayer dielectric (ILD) layers to accommodate the high speed signals. The use of the copper and low-k interlayer dielectric layers reduces the resistance of the metal interconnects and the capacitance between the metal interconnects to enable the high speed signals to be transmitted. Because low-k interlayer dielectric layers are affected by similar process techniques that are used to pattern and remove other layers used to create a semiconductor device, the low-k interlayer dielectric layer is susceptible to being altered from the shape or characteristics the layer was designed to exhibit.
A current solution to protect a low-k interlayer dielectric layer is to form a hard mask layer over a low-k interlayer dielectric to protect the low-k interlayer dielectric layer from processes performed on other layers. For example, an anti-reflective layer and a photoresist layer may be formed over an interlayer dielectric layer for patterning the interlayer dielectric layer as necessary to form a semiconductor device. Once the low-k interlayer dielectric layer is patterned, the remaining photoresist and anti-reflective layer must be removed. In the absence of using a hard mask layer that separates the interlayer dielectric layer from the anti-reflective and the photoresist layers, an etch process or a chemical mechanical polishing process performed to remove an anti-reflective layer and a photoresist layer would result in degradation of the interlayer dielectric layer. As mentioned above, the degradation results because the chemistries that are used to etch or remove photoresist and anti-reflective layers are the same chemistries that may be used to remove an ILD layer. Therefore, the characteristics or dimensions of the patterns in the ILD may be significantly altered during the etching or removal of an anti-reflective and photoresist layers. This ultimately would result in unreliable operation of semiconductor devices or low manufacturing yields of properly operating semiconductor devices. Therefore, the use of a hard mask is needed to protect the ILD layer from the processes used to alter other layers.
Problems arise in the use of a hard mask when the material used for the hard mask reacts with the layer deposited above the hard mask. Such a reaction may create a strong adhesion between the hard mask and the upper adjoining layer, such as an anti-reflective layer, making an adjoining layer more difficult to remove. Therefore, a more aggressive chemistry must be used, longer exposure to a removal process must be used, or a combination of an aggressive chemistry and longer exposure to a removal process must be used to remove the upper layers from the hard mask. The use of a more aggressive chemistry and longer exposure to a removal process results in excessive degradation of an interlayer dielectric layer. Such degradation includes the interlayer dielectric layer unpredictably undercutting the hard mask. Because degradation of the interlayer dielectric layer, such as undercutting, effects the characteristics and dimensions of the interlayer dielectric layer the operating characteristics of a semiconductor device and reliability of a semiconductor device are degraded.